High-efficiency ∼2 µm CW laser operation of LD-pumped Tm³⁺:CaF₂ single-crystal fibers

Abstract

The Tm:CaF 2 single-crystal fibers were successfully grown by modified temperature gradient technique method. The J-O intensity parameters, spontaneous radiative transition rates, radiative lifetimes and fluorescence branching ratios of Tm 3+ were calculated with Judd-Ofelt theory. A systematic study of the fluorescence characteristics has been carried out. Simulated emission cross-sections of the 3 F 4 → 3 H 6 transition were calculated to be 6.68×10 −21 cm −2 and 4.65×10 −21 cm −2 for crystal doped with 3 at.% and 4 at.% Tm 3+ . The 64.4% slope efficiency with output power of 2.23W was achieved in 3 at.% Tm:CaF 2 single-crystal fiber. The slope efficiency decreased to 44.5% and maximum output power decreased to 1.65W in 4 at.% Tm:CaF 2 single-crystal fiber. Obtained results show that Tm-doped CaF 2 single-crystal fibers are promising materials for IR laser action generation.